1. Field of the Invention
The present invention relates to a rapidly cured, highly tintable, mar resistant coating composition and for the coatings produced thereby. The coatings are used for polymeric substrates, particularly ophthalmic lenses, and more particularly polycarbonate ophthalmic lenses, to which a subsequently applied antireflective coating may be applied with excellent adhesion.
2. Background of the Art
Polymeric materials have numerous advantages over glass in terms of impact resistance, weight, cost, ease of manufacture, and other aspects, for which reason polymeric materials are commonly used to manufacture a great many products worldwide. However, in many applications, the use of a polymeric material necessitates the use of one or more coatings in order to obtain properties, such as mar resistance, tintability, optical properties, and other features, that are required for a particular application. For this reason, coatings for polymeric materials are of great interest and a great deal of effort has been exerted in this area.
Until recently, there have been primarily two general types of transparent coatings that have been employed on polymeric substrates that allow the transparent properties of the polymeric materials to be utilized. These two general categories include the radiation cured coatings and the thermally cured coatings. Coatings of the former type usually contain acrylate or acrylate and oxirane functional compounds that are polymerized on exposure to radiation of a particular wavelength that is capable of acting upon a polymerization initiator to commence polymerization. Coatings of the latter type usually contain siloxanes or other organometallic materials and metal oxides that are polymerized on exposure to heat, which may come from a variety of convection, radiant, or other sources.
The advantages of the radiation cured coatings include good coating stability, very rapid cure in under one minute at relatively low temperature, primerless adhesion to many substrates, rapid dye absorption in a tinting process, and the potential for very low solvent concentration so as to allow for a minimal amount of emissions of volatile organic compounds. The disadvantages of this type of coating include relatively poor mar resistance and poor adhesion of subsequently applied antireflective coatings. Though fewer in number than the advantages, these disadvantages are very serious in demanding applications requiring these properties, which thus severely limits the use of these coatings.
The advantages of the thermally cured coatings include superior mar resistance and they serve as an excellent base for subsequently applied antireflective coatings of any type. The disadvantages of this type of coating include long cure times over several hours at elevated temperatures, relatively little dye absorption, and poor adhesion, such that a primer is usually required unless the formula is modified so as to obtain primerless adhesion at the expense of solution stability.
These two types of coatings are at opposite extremes. What is desired, particularly in the ophthalmic lens industry, is a coating solution that is very stable at room temperature, has excellent adhesion to all common polymeric substrates without the use of a primer, will cure very rapidly in a few seconds to give a coating that can be tinted very quickly, has better mar resistance than the present radiation cured coatings, and provides an excellent base for an antireflective coating of any variety. The present invention provides for just this combination of properties, which heretofore has not been found.
Previous attempts have been made by others to achieve a compromise to incorporate the benefits of both types of coating into one. One approach has been to incorporate very fine particles of silica or metal oxide into a radiation curable coating. This approach has had very limited success since, even at high concentrations of particles, the properties of the coating tend to mimic those of the continuous organic phase, not the disperse phase. This format of mar-resistant or abrasion resistant coatings are shown in such disclosures as U.S. Pat. Nos. 4,073,967; 6,951,894; 5,744,243; 5,624,757; and 5,723,175.
Another approach has been to use siloxane monomers with organofunctional moieties that can be exploited for rapid radiation cure. This approach avoids the formation of a dual phase system and thereby has the potential for better coating performance in the cured film. However, previous efforts in this area have resulted in poor solution stability and high viscosity requiring compromises in performance properties such as mar resistance or tintability. In the above approach, U.S. Pat. No. 6,100,313 (Treadway) teaches the use of one or more polymerizable ethers. The coatings of the present invention specifically avoid the use of these materials due to their known deleterious effect on adhesion, mar resistance, and durability on exposure to ultraviolet light. Furthermore, some of these materials are known to have serious adverse health effects. Instead, other materials previously not known to be beneficial have been used to enhance the dye absorption of the coatings of the present invention without adversely affecting the adhesion, mar resistance, and exterior durability.
Both U.S. Pat. No. 6,780,232 (Treadway) and U.S. Pat. No. 7,037,585 (Treadway) teach the use of an unhydrolyzed oxirane functional siloxane that is added to reduce the viscosity of the coating solution and effectively reduce the extent of hydrolysis, as without this measure these coatings tend to have poor stability with respect to viscosity. All Patents and applications and texts cited herein are incorporated in their entirety into this application.